I was working on a 6V6 amp the other day, and wanted to test the tubes on my newfangled tube tester. The tester works fine, I've tested other tubes with it, but this was the first time I tried 6V6.
So, no short circuits, and emission quality seems fine, but when measuring gm I can't even dial in the meter. Everything seems *dead*.
My tester manual indicates 100V plate and 100V screen when testing these, as well as a grid voltage of -4.5V. So I tried 250/100 on plate/screen, and grid at 0V. I got some reaction, but still not enough to zero in the tester.
Ok, these tubes were bummers i thought, so I bought new ones - however, these measured just as bad. The tubes work fine in circuit, though.
I've double checked that all settings on the tube tester are ok, all pins properly configured. So I was wondering, how come I'm not able to test 6V6s? Could there be some weird fault in my tester? Or am I holding it wrong(tm)?
Any insights would be very much appreciated!
So, no short circuits, and emission quality seems fine, but when measuring gm I can't even dial in the meter. Everything seems *dead*.
My tester manual indicates 100V plate and 100V screen when testing these, as well as a grid voltage of -4.5V. So I tried 250/100 on plate/screen, and grid at 0V. I got some reaction, but still not enough to zero in the tester.
Ok, these tubes were bummers i thought, so I bought new ones - however, these measured just as bad. The tubes work fine in circuit, though.
I've double checked that all settings on the tube tester are ok, all pins properly configured. So I was wondering, how come I'm not able to test 6V6s? Could there be some weird fault in my tester? Or am I holding it wrong(tm)?
Any insights would be very much appreciated!
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It would help if you gave the model and make of the tube tester.
There is a whole multitude of testers old and new and no they don't all test for GM the same way .
To narrow this down does a 6L6 tube work okay or not or a 6F6-EL33-EL35-EL37-KT61-KT66 ?
If the others work okay then you have a problem with your selector switch whichever type it is as you have yet to tell us .
There is a whole multitude of testers old and new and no they don't all test for GM the same way .
To narrow this down does a 6L6 tube work okay or not or a 6F6-EL33-EL35-EL37-KT61-KT66 ?
If the others work okay then you have a problem with your selector switch whichever type it is as you have yet to tell us .
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TTL I don't think you have worked out the reason I asked --specifically -- whether the tubes quoted work or not so I will give you more information .
The IO8 based based tubes you used as a test are TRIODES therefore they are not the same connections underneath in the wiring -6SC7 /6SF5 so that is no judgement on whether its okay or not .
But it is a help your IO8 base is faulty --replace it , its been used so much that the contacts in the base are worn --no DON'T "spray it " - its not a potentiometer --replace it .
Its not as big a job as you think its very like my old UK tube tester a Taylor 45C but actually better made and I have seen the inside of your tester you should have no problem replacing it.
Take my word on this buy the best and dearest ceramic IO8 base this is a tube tester you are working on not an audio amplifier I have replaced many tube tester bases with the same fault as IO8 based tubes were used from the later 30,s up to the late 40,s so it would be used to test a lot of tubes -- don't buy cheap plastic rubbish .
The IO8 based based tubes you used as a test are TRIODES therefore they are not the same connections underneath in the wiring -6SC7 /6SF5 so that is no judgement on whether its okay or not .
But it is a help your IO8 base is faulty --replace it , its been used so much that the contacts in the base are worn --no DON'T "spray it " - its not a potentiometer --replace it .
Its not as big a job as you think its very like my old UK tube tester a Taylor 45C but actually better made and I have seen the inside of your tester you should have no problem replacing it.
Take my word on this buy the best and dearest ceramic IO8 base this is a tube tester you are working on not an audio amplifier I have replaced many tube tester bases with the same fault as IO8 based tubes were used from the later 30,s up to the late 40,s so it would be used to test a lot of tubes -- don't buy cheap plastic rubbish .
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I think duncan2 is right. I have seen this on other testers too. The Hickok 539C I normally borrow from a friend of mines needed sockets replacement soon after he bought it. This tester was basically NEW, it came from a school for technicians where it had been in box for decades. Both the octal and the noval sockets, after a short period of use, started to have contact issues. Replaced the sockets, everything was fine.
Tester sockets have to handle 100's or 1000's of insertion cycles - that's a whole different game from an in-circuit socket that might see half-a-dozen insertion cycles at most, thus a standard socket is unlikely to survive in a tester.
I don't know if they make ZIF sockets for valves, but if they do that would be the best option if designing test-gear from scratch.
I don't know if they make ZIF sockets for valves, but if they do that would be the best option if designing test-gear from scratch.
Continuity between the pins of that socket and other sockets measure fine - I even put a tube only partially in, so I could measure continuity directly from the pins of the tube to the other sockets, and that seemed fine as well. Could it still be a worn socket?
Once you fix it, use these socket savers and never have that problem again.
Search | Amplified Parts
https://www.amazon.com/Cary-Bakelite-Vacuum-Socket-Testing/dp/B00KPBOGHW
Search | Amplified Parts
https://www.amazon.com/Cary-Bakelite-Vacuum-Socket-Testing/dp/B00KPBOGHW
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Look TTL its one thing testing using a digital ohmmeter outputting microamps and higher current and voltage loads in a real situation .
Partially in is not full contact its when its in fully it wont register - your voltage selector switches work okay with other sockets and different types ( based ) tubes.
To try to explain the function of your switches when set to =Anode/Plate-- ALL the bases are " looped "series connected its just a matter of one of the selector switches be it Plate-Grid 2 ( screen ) -Grid 3 etc etc to the correct position on each tube .
This is done in different ways and digitally in some modern designed DIY tube testers .
Thats why I ASKED you but you ignored me when I asked you to try the other tubes I posted on post #2 --they ALL have the same base connections .
I am not going to ask you again to change the socket its up to you but I have rebuilt several tube testers and I am very conversant with their function.
Partially in is not full contact its when its in fully it wont register - your voltage selector switches work okay with other sockets and different types ( based ) tubes.
To try to explain the function of your switches when set to =Anode/Plate-- ALL the bases are " looped "series connected its just a matter of one of the selector switches be it Plate-Grid 2 ( screen ) -Grid 3 etc etc to the correct position on each tube .
This is done in different ways and digitally in some modern designed DIY tube testers .
Thats why I ASKED you but you ignored me when I asked you to try the other tubes I posted on post #2 --they ALL have the same base connections .
I am not going to ask you again to change the socket its up to you but I have rebuilt several tube testers and I am very conversant with their function.
To be absolutely certain that there is nothing wrong with your tube tester just take pencil and drawing paper and measure, using a simple setup, and choose one 2nd screen voltage and plot the 1st (signal) screen vs plate voltage
with that 6V6 tube. Then see if there comes out a good characteristic.
with that 6V6 tube. Then see if there comes out a good characteristic.
duncan2, it was not my intention to ignore you! The reason I didn't try the tubes you mentioned, is simply because I don't have them. Most of my tubes are noval. I'll scour my boxes and see what I have of IO8's -- perhaps I can find something equivalent enough.
For those looking for the pin selector codes and circuit diagram for the tubes , its in French but you can still figure out the adjustments as the lettering is alphabetical for various tubes-
https://www.radiocollection.be/images/mesure_img/centrad752.pdf
https://www.radiocollection.be/images/mesure_img/centrad752.pdf
Excellent, thanks! Hereby ordered!
As for replacement sockets, I managed to get a regional tube amp repair shop to sell me a few - so hopefully they're of proper quality (at least better than what I would manage to whip up from AliExpress).
If I'm lucky, they'll arrive before weekend. There's also a shipment of mixed used tubes I managed to "score" arriving today, perhaps I get some more IO8 pentodes to test with.
While we're at it, are there any other socket types I should suspect are well beyond their life?
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Yes the modern B9A based tubes used extensively from the early 50,s onwards others like the B8A less so as well as the B7G .
No the B9A is the main one after the !O8 base.
No the B9A is the main one after the !O8 base.
I've now replaced the IO8 socket, but behaviour is the same as before. Where would be a good idea to have a look?
In that case the selector switches that make up the correct positioning of the contacts to the 6V6 configuration which is = OFA--SGO-- MKO has dirty or broken contacts .
That is in numerical order =123--456-789 positioning of the SELECTOR switches.
That is in numerical order =123--456-789 positioning of the SELECTOR switches.
If you are testing a 6V6 with 100v on the screen, you will get only small plate current and the tube will appear bad.
Yes it should be set at =200-200 which is the highest voltage available ( switch at LHS of meter).